#include<iostream>
#include<cmath>
#include<cstdio>
using namespace std;
int main()
{
	double f1, f2, ans;
	int n;
	cin >> n;
	f1 = (1 + sqrt(5)) * 1.0 / 2;
	f2 = (1 - sqrt(5)) * 1.0 / 2;
	ans = pow(f1, n) - pow(f2, n);
	ans /= sqrt(5);
	printf("%.2lf", ans);
	return 0;
}